Phase Equilibria of the In-Pd-Sn System at 500 °C and 800 °C: Experimental Study and CALPHAD Modeling

Phase equilibria in the In-Pd-Sn system were investigated by a combination of key experiments and thermodynamic modeling. Partial isothermal sections at 500 °C and 800 °C of the In-Pd-Sn system for Pd contents above 66 at.% have been plotted experimentally using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). The solubility of the third component in binary compounds InPd₃ and Pd₃Sn was determined. The new ternary compound τ₁ was found in Pd contents ranging from 20 to 25 at.% and at Sn contents varying from 5 to approximately 17 at.% Sn. This compound crystallizes in an Al₃Ti-type tetragonal structure. Isostructural InPd₂ and Pd₂Sn phases from the In-Pd and Pd-Sn binary compositions form a continuous phase field in the ternary system at both temperatures. The temperatures of the solidus, liquidus, and phase transitions of the alloys along the Pd-In50Sn50 line were measured using DTA/DSC. Thermodynamic calculation of the In-Pd-Sn ternary system is performed using the CALPHAD method using the Thermo-Calc^® software. The thermodynamic properties of the disordered fcc and liquid phases were described by the Redlich-Kister-Muggianu model. To describe intermetallic phases, namely, InPd₃, Pd₃Sn, τ₁ and Pd₂(In_xSn_1-x), a two-sublattice models was used. Thermodynamic description of the In-Pd-Sn system obtained in this study is in good agreement both with our results and the published experimental data.